It is good you are thinking about a MBA at this point in your life. This will give you plenty of time to fine-tune your career expectations and goals, and to position yourself for the strongest application possible. Having the GMAT out of the way early is a big plus!
1. 2 years may be a bit on the short side...if you plan on only having 24 months experience when you enter school, that pretty much means you will be working on apps shortly after your first year. Will you have enough professional experience to write a good set of essays? It is certainly possible, and people have gotten into the top programs with only two years, but I don't think it would be a cakewalk by any stretch. As a young applicant, schools will tend to focus more on your undergrad experience. Hopefully you are well stocked with ECs...
2. Many people get a MBA to switch careers. I have heard stories of engineers and military pilots who switch into finance. If your will is strong enough, you will end up where you want.
3. Are you looking for a part-time program? I can't comment too much on those, especially UMiami. Certainly, some of the best finance programs in the country are located in New York, Philadelphia and Chicago.
Right now, your goals are still a bit vague, and it is hard to project a good range of schools for you at this point. However, sounds like you are still very young, and have plenty of time to figure things out. Seek out leadership positions and develop your own personal interests into ECs if you can...these things can only help you out down the road!